Previously, a LED lamp using a LED chip has been utilized in many fields, such as a signal lamp, a portable telephone, various electric spectaculars, an in-car indicator, various display systems and the like. Then, there has been a light emitting device formed by combining a LED chip and a fluorescent particle(s). The fluorescent particle(s) emits light excited by light emitted from the LED chip and thereby having a color different from the light emitted from the LED chip. Then, research and development of such a light emitting device have been worked in various places. As this kind of light emitting device, for example, a white light emitting device (generally, called a white LED) has been adopted on a commercial basis, and can obtain white light (emission spectrum of white light) by combining a LED chip and a fluorescent body, and then increasingly has been applied to a backlight of a liquid crystal display and a flash unit.
Then, recently, the white LED has been souped-up. So, research and development for utilizing the white LED for illumination purpose have been worked increasingly. The white LED has a long life and is mercury free, and thus has been expected as an environmentally-friendly alternative light source for a fluorescent lamp, by utilizing such an advantage.
As the above-mentioned white LED, for example, there has been a light emitting device (for example, see Japanese Patent Application Laid-Open No. 2007-324475), which is formed by combining a LED chip emitting blue light and a wavelength conversion member (a color conversion member). Here, the wavelength conversion member is formed by dispersing a wave-length conversion particle formed by using a fluorescent particle (a red fluorescent particle, a green fluorescent particle) into a translucent medium (a silicone resin, a glass and the like).
Here, the wavelength conversion member disclosed in the document is formed by using the fluorescent particle (red fluorescent particle, green fluorescent particle) covered by a translucent coated layer as the wavelength conversion particle, and the translucent coated layer is formed of a material having a refraction index midway between refraction indexes of the fluore-scent particle and the translucent medium. Then, the wavelength conver-sion member can improve incident efficiency of light emitted from the LED chip incident upon the fluorescent particle (incident efficiency of exciting light incident upon the fluorescent particle) and efficiency for extracting conversion light from the fluorescent particle.
However, as shown in FIG. 8A, in the wavelength conversion member described in the above document, when a refraction index of a fluorescent particle 171 is denoted by n11 and a refraction index of a translucent medium 173 is denoted by n13 and a refraction index of a translucent coated layer 172 is denoted by n12, n13<n12<n11 is satisfied. Then, as shown in FIG. 8B, these refraction indexes change in stages with respect to a normal direction of a surface of fluorescent particle 171. In this wavelength conversion member, in regard to a part of exciting light emitted from the LED chip, Fresnel reflection occurs at an interface between translucent medium 173 and translucent coated layer 172, and at an interface between translucent coated layer 172 and fluorescent particle 171. Thus, it is expected that the incident efficiency of the exciting light incident upon fluorescent particle 171 is further improved. Then, in the wavelength conversion member, refra-ction index n12 of translucent coated layer 172 is set to be smaller than refraction index n11 of fluorescent particle 171. As a result, in regard to the conversion light from fluorescent particle 171, total reflection occurs at an interface between translucent coated layer 172 and fluorescent particle 171 and, that is, there is an angle of total reflection. Accordingly, it is expected that the efficiency for extracting the conversion light from fluorescent particle 171 is further improved.